Fixed a bug in zend_memnistr

add test GH-12457

Author: SakiTakamachi

Zend/tests/gh12457.phpt

@@ -0,0 +1,12 @@
+--TEST--
+GH-12458 (Fix GH-12457: Fixed a bug in zend_memnistr)
+--FILE--
+<?php
+var_dump(stripos('aaBBBBBb', 'b'));
+var_dump(stripos('aaBBBBBbb', 'b'));
+var_dump(stripos('aaBBBBBbbb', 'b'));
+?>
+--EXPECTF--
+int(2)
+int(2)
+int(2)

Zend/zend_operators.h

@@ -945,7 +945,7 @@ zend_memnistr(const char *haystack, const char *needle, size_t needle_len, const
 	const char *p_upper = NULL;
 	if (first_lower != first_upper) {
 		// If the needle length is 1 we don't need to look beyond p_lower as it is a guaranteed match
-		size_t upper_search_length = end - (needle_len == 1 && p_lower != NULL ? p_lower : haystack);
+		size_t upper_search_length = needle_len == 1 && p_lower != NULL ? end - haystack : p_lower - haystack;
 		p_upper = (const char *)memchr(haystack, first_upper, upper_search_length);
 	}
 	const char *p = !p_upper || (p_lower && p_lower < p_upper) ? p_lower : p_upper;